1. Field of the Invention
The present invention relates to a printing medium feeding method for feeding a printing medium, which is a subject of conveyance, in association with a conveyance operation of conveying the printing medium to a predetermined print start position, and a printing apparatus.
2. Description of the Related Art
There is a printing apparatus that includes a device for feeding cut-sheet printing media one by one to a print position at which printing is carried out by a printing unit such as a printing head. Here, the printing media not only mean paper but also widely include sheet media made of various materials usable for printing, such as clothes and plastic films. In the following description, these printing media may be simply referred to as a sheet. In this regard, operations of feeding and discharging such a printing medium may also be referred to as paper feed and paper discharge, respectively.
A paper feeder of this type has a configuration in which conveyance force is given to a sheet S by bringing a paper feed roller 2 into pressure-contact with the sheet S as shown in FIGS. 5A to 5F, for example. Additionally, such a paper feeder has a configuration in which a conveyance load is given to the sheet S by a separation unit 7 including a separation pad, a separation claw, a separation projection, and the like, so as to separate only the uppermost sheet S among sheets S stacked on the paper feeder from sheets thereunder. The separated sheet S is conveyed to a conveyance roller 11 located at the upstream side in conveyance direction by clockwise rotation of the paper feed roller 2 (FIGS. 5A to 5C). When the paper feed roller 2 completes one rotation, the pressure-contact with the sheet S is released (FIG. 5E). After that, the sheet S is conveyed to a predetermined print start position only by the conveyance roller 11 (FIG. 5F).
Japanese Patent Laid-open No. 2002-205838 discloses a sheet feeder in which a sheet is conveyed after the sheet is started to be fed by a paper feed roller and then abuts a stopped conveyance roller for registration. The sheet makes a loop by being pressed to the conveyance roller. After that, a position of the sheet is corrected so that the leading edge of the sheet can be parallel with the conveyance roller. Then, the sheet is conveyed by the paper feed roller and conveyance roller to the print start position. In the following description, such a paper feeding method is referred to as “registration paper feed”.
In addition, Japanese Patent Laid-open No. 2002-187634 discloses a method in which conveyance roller is configured to have already started rotating by the time a leading edge of a sheet started to be fed by a paper feed roller reaches the conveyance roller, and then the sheet is conveyed to a print start position with no interruption. At this time, in order to supply a sheet without causing paper jam, the paper feed and the conveyance rollers are rotated at the same rate. In the following description, this paper feeding method is referred to as “non-registration paper feed” after Japanese Patent Laid-open No. 2002-187634. Although accuracy of positioning a sheet to a print start position with the “non-registration paper feed” is lower than that with the “registration paper feed,” there is an advantage that time required for feeding can be reduced.
Japanese Patent Laid-open No. 2004-082640 discloses “simultaneous control of paper feed and discharge” in which a paper discharge operation of an already-printed sheet (current page) and a paper feeding operation of a sheet to be printed next (next page) are simultaneously carried out, when printing is continuously carried out on multiple sheets. If this control is applied to “non-registration paper feed,” as shown in FIG. 7A, an image is printed on a sheet SA being the current page, and feeding of a sheet SB being the next page is started at the timing when printing of final data onto the sheet SA is completed (FIG. 7B). Thereby, the operation of discharging the sheet SA being the current page and the operation of conveying the sheet SB being the next page to a print start position can be simultaneously carried out (FIGS. 7B to 7G). As a result, a distance between the trailing edge of the sheet SA being the current page and the leading edge of the sheet SB being the next page is set to be small, so that a printing rate of continuous printing on multiple sheets can be improved.
However, in order to carry out printing at a higher rate in the above-described “non-registration paper feed”, rotational rates of both the paper feed and the conveyance rollers need to be improved similarly to each other. For this reason, it is also necessary to improve performances of a feed motor, which is a driving source for the paper feed roller, and a conveyance motor, which is a driving source for the conveyance roller. However, this results in an increase of the manufacturing cost of the printing apparatus. There is also a problem, particularly a problem with the conveyance motor, that a temperature rise causes a reduction in torque when an inexpensive motor is used, because the conveyance motor continues to perform a conveyance operation even when an image with a small amount of data is continuously printed.
In addition, in order to carry out printing at a higher rate in the above-described “simultaneous control of paper feed and discharge”, rotational rates of both the paper feed and the conveyance rollers have to be improved similarly to each other. Accordingly, the rate of discharging the sheet being the current page is also increased and the discharged sheets are untidily stacked on a paper tray or the like. As a result, this causes a problem of deteriorating alignment of discharged sheets. Furthermore, if printing data is present near the trailing edge of the sheet, there arises a problem that a distance between the trailing edge of the sheet being the current page and the leading edge of the sheet being the next page cannot be reduced.